One of the more common solutions to any of the above mentioned conditions involves a surgical procedure known as spinal fusion. A spinal fusion procedure involves fusing two or more vertebral bodies in order to eliminate motion at the intervertebral disc or joint. To achieve this, natural or artificial bone are placed between the vertebrae and frequently a hardware is used to instrument the involved vertebrae to avoid movement and in this way facilitating fusion. In this way damaged or diseased vertebrae are connected to healthy adjacent vertebrae to stabilize the spine while the bone grows and fusion takes place.
The mechanical hardware used to immobilize the spinal column typically involves a series of bone screws and metal rods or plates. When the spine surgery is posteriorly performed, one of the common practices is to place bone screws into the vertebral bodies and then connect a metal rod (usually of titanium or chromium-cobalt alloy or steel) between the bone screws thus creating a rigid structure between adjacent vertebral bodies.
Current systems perform a segmental correction of the curvatures of the spine, immobilizing a group of vertebrae of the spinal deformity center, regardless of the fact that as it is well known scoliosis deformity is a rotating deformity with maximum rotational deformity at the central vertebra of the curve and this deformity decreasing progressively towards the curve ends (periphery), so that the correction required in each vertebrae included in the curve deformity is different and various corrective forces are needed at each level.
Several approaches in the field are following detailed:
A spinal stabilization system suitable for performing spine surgery appears disclosed in EP 2366349, U.S. Pat. No. 7,563,264 and U.S. Pat. No. 7,491,218, where a bone fastener assembly with a collar that allows for angulation of a bone fastener relative to the collar in a conical range of motion is revealed. U.S. Pat. No. 7,914,558 and U.S. Pat. No. 7,691,132 disclose a similar method for inserting a spinal stabilization system in a human spine.
U.S. Pat. No. 8,147,524 refer to a method of reducing a spinal deformity where a pair of bone anchors is attached of each of the vertebrae of the spinal section injured and the pair of bona anchor are interconnected with a bridge member to which correction metal rods as previously referred are attached.
US 2011/0319938 disclose a coplanar deformity correction system involving a bone anchor assembly including a bone anchor, a receiver mounted to the bone anchor, a saddle within the receiver, a spacer within the receiver and an engaging member.
U.S. Pat. No. 8,221,474 reveals a method for assembling a system for correcting alignment of a spinal column of a patient using a des-rotation handle to a transverse bridge between first and second implant holders attached to a vertebra.
FR 2971698 disclose a device for the correction of spine deformations comprising pedicle screws arranged to be connected by a rod bent implantable, rods intended to be engaged through different tubular elements to align corresponding to the correction of said spine, by translation, rotation and rocking of the vertebrae.
U.S. Pat. No. 8,221,426 disclose a spinal alignment system comprising a plurality of pedicle assemblies including pedicle posts and adapter to couple the pedicle posts and a holder to couple to the adapter.
The system of this invention applies the mechanical correction that specifically requires each vertebra.
EP 1774919 refers to a bone anchoring device revealing anchoring elements for a spinal alignment system wherein the movement of the anchoring element before locking is limited to a single plane by a form-fit connection between a head of the anchoring element an a pressure element.
Cited current systems use for the correction of spinal deformities pedicle screws and extenders thereby improving the lever arm to apply corrective forces, but all systems apply the same methodical correction to both sides of the spine, and this despite the fact that convex side and the concave side have opposite deformities. The convexity of scoliosis has an increased posterior perimeter (the lengths between posterior elements is increased) and presents a relative kyphosis deformity, while in the concave side the posterior perimeter is shortened and in addition is lordotic. Therefore, these differing deformities require unlike correctives forces to be applied on both sides, and this approach on which is based this invention has not been applied previously.
According to the inventors also no current system performs a preoperative calculation of the correction to be applied in each patient with scoliosis.